The combined firm will be known as Banyan Partners LLC and will have some $3.4 billion in assets under management, according to the firms’ executives. Peter Raimondi, chief executive officer of Banyan Partners, will stay in that position at the new firm, while Tom Manning, CEO and chief investment officer of Silver Bridge, will become chief investment officer of the combined firm.

The deal, which will be announced Tuesday, is expected to close in August.

Banyan and Silver Bridge, which have $1.5 billion and $1.9 billion in assets, respectively, had been in talks for nearly six months. “There are many firms in the $1.5 billion space that find it difficult to grow and lack resources,” said Manning in a telephone interview. He added that the combination of the two firms will create a “powerful” registered investment adviser.

Raimondi said he expects the new firm to grow assets and revenue between 20% and 30% annually.

The new firm will blend Banyan’s focus on stocks and options and Silver Bridge’s focus on fixed income, in-house tax preparation and wealth management, said Raimondi, adding that Banyan had been searching for a partner to expand the wealth-management component of its business.

At a wealth-management firm, relationship managers focus on a client’s entire financial plan, not just the investment portion of it.

Most of the firms’ clients have assets in the $2 million to $10 million range. The combined firm plans to cater to those with as little as $1 million up through more than $100 million, the executives said.

Banyan has made four acquisitions over the past five years, but has walked away from “three times as many” because they weren’t “the right culture fit,” said Raimondi.

Registered investment advisers’ share of industry assets grew to 12.2% in 2011, up from 10.8% in 2010, according to data from Cerulli Associates, a Boston-based analytics firm.